JPH0760509B2 - Magnetic recording medium - Google Patents

Description

TECHNICAL FIELD The present invention relates to a magnetic recording medium used for a magnetic card or the like.

2. Description of the Related Art In recent years, magnetic cards have been remarkably popularized and used in various fields. In addition to conventionally used bank cards and credit cards, recently, so-called security cards are used more and more. If the information is easily tampered with, this will significantly reduce the reliability of the system. Therefore, a magnetic card having a protection function for preventing falsification of information is desired, and magnetic cards having various structures have been proposed and used. Among these, as a magnetic recording medium suitable for use in a magnetic card or the like to provide this kind of protection function, a high coercive force layer, a low coercive force layer, and a high magnetic permeability layer are sequentially laminated on a substrate. Is proposed.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention However, in the case of the conventional magnetic recording medium of this type, when the magnetic recording medium is used in a magnetic card or the like, it is possible to use the magnetic recording medium without trouble and to further protect the information from falsification. To enhance it, its high coercive force layer, low coercive force layer,
The material for forming the high-permeability layer and how to select the magnetic properties have not been sufficiently clarified. In addition, the current situation is that the magnetic card cannot be effectively prevented from being tampered with as a magnetic card.

In view of such a conventional technique, the purpose of the present invention is to
It is an object of the present invention to provide a magnetic recording medium that can be used as a magnetic card that is difficult to falsify information without trouble.

According to the present invention, in a magnetic recording medium in which a high coercive force layer, a low coercive force layer, and a high magnetic permeability layer are sequentially laminated on a substrate, the high magnetic permeability layer is In a low coercive force layer and a high coercive force layer formed of a material capable of giving a coercive force of 20 Oe or less sufficient to exert a shield effect for information recorded in the high coercive force layer, the high coercive force layer, Is formed of a material capable of recording information with a magnetic head against the shield effect against an external magnetic field and capable of giving a coercive force of 2000 Oe or more and 5000 Oe or less so as not to be easily accidentally demagnetized, and the low coercive force layer is formed. , 500 Oe or more and 1500 Oe or less so that information can be recorded by the magnetic head against the shielding effect against the external magnetic field by the high magnetic permeability layer and without affecting the information recorded on the high coercive force layer thereunder. Can give a magnetic force Made of material.

Examples Next, the present invention will be described in more detail with reference to the accompanying drawings with reference to the examples of the present invention.

Therefore, the present inventor first examined in detail the magnetic characteristics required for each magnetic layer of the conventional magnetic recording medium of this kind as described above and the magnetic material effective for them.

FIG. 1 partially shows an enlarged cross section when a magnetic recording medium as an embodiment of the present invention is used as a magnetic card. In this magnetic recording medium, a high coercive force layer 4, a low coercive force layer 3, a high magnetic permeability layer 2 and a protective layer 1 are sequentially laminated on a substrate 5.

First, the high coercive force layer 4 preferably has a high coercive force within a range recordable by the magnetic head and has a coercive force that is not demagnetized by an ordinary magnet in order to prevent a data demagnetization accident. Generally, the strength of the magnetic field generated from the vicinity of magnets used in daily life is 2000 Oe or less,
Further, considering that the coercive force that can be currently recorded by the magnetic head is 5000 Oe or less, the coercive force of the high coercive force layer 4 is
2000Oe to 5000Oe is required.

On the other hand, the low coercive force layer 3 needs a coercive force that does not affect the high coercive force layer 4 during recording. For this purpose, the coercive force needs to be 1500 Oe or less. In addition, considering that 500 Oe or more is required to remove the shield of the high magnetic permeability layer 2, the coercive force of the low coercive force layer 3 is 500 Oe.
e to 1500 Oe is required.

The magnetic card is required to have flexibility in consideration of the purpose of use and the state of use, and in order to maintain such flexibility, the high magnetic permeability layer 2 should have a high magnetic permeability of metal such as permalloy or sendust. materials and M _n -Z _n must be formed by dispersing a powder of ferrite or metal amorphous material such as ferrite. The coercive force of the high-permeability layer 2 formed of such a material is about 20 Oe at maximum. Such a value of the coercive force is sufficient to obtain the desired shield effect. Then, the magnetic field required to break the shield by the high magnetic permeability layer 2 is required to be 500 Oe or more.

From the above, the coercive force required for each layer is as follows.

High coercive force layer 2000Oe to 5000Oe Low coercive force layer 500Oe to 1500Oe High magnetic permeability layer 20Oe or less Next, considering the forming materials of each layer, the forming materials of the high coercive force layer 4 are Ba ferrite powder, Sr ferrite powder, and metal powder. various things can be considered like, also, as the material for forming the low coercive force layer 3, Ba ferrite powder, Sr ferrite powder, C _o deposition [gamma] F _e2 O _3, can be considered a variety, such as metal powder. However, considering the above-described data recording method and protection function of the magnetic recording medium of the present invention, it is necessary that the material satisfy the following conditions.

(1) Excellent squareness. It is important that the coercive force distribution is sharp in order to enable recording by utilizing the difference in coercive force of each layer. For this purpose, highly anisotropic and highly oriented materials are preferred.

(2) For the purpose of preventing forgery, it is not possible to easily determine that different types of magnetic materials are formed in multiple layers. That is, if there is a difference in the shape of powder, constituent elements, and type of magnetic material, it is possible to easily discriminate that there is a multi-layer, and the operating principle can be inferred.

Ba ferrite powder and Sr ferrite powder have large crystal magnetic anisotropy and excellent orientation, so that they can form a coating film with good squareness, and thus satisfy the condition of (1) above. It is a preferable material for forming the high coercive force layer and the low coercive force layer.

In addition, since the coercive force of the coating film in which Ba ferrite powder is dispersed can be arbitrarily controlled from 500 Oe to 5000 Oe,
It is possible to provide a high coercive force layer having the preferable coercive force as described above and a low coercive force layer having the preferable coercive force as described above. When the high coercive force layer and the low coercive force layer are formed of a coating film of Ba ferrite powder having the same shape, it may be impossible to determine that they are formed in two layers in cross section. It can be confirmed that it cannot be confirmed by elemental analysis. This satisfies the condition (2) above.

Next, in order to confirm that the magnetic characteristics of each layer and the specification of the forming material in the magnetic recording medium of the present invention as described above exhibit a remarkable effect, various magnetic cards were prepared and tested. The results obtained will be explained.

Experimental Example I Using 7 kinds of magnetic powders having different coercive force, a coating material was prepared with the composition shown below, coated on white PET, dried and punched out to prepare 7 kinds of magnetic cards.

Magnetic powder 100 parts by weight S-Lec A (vinyl chloride resin, Sekisui Chemical Co., Ltd.) 17 parts by weight Nipporan 2304 (urethane resin, polyurethane polyurethane) 47 parts by weight Surfactant 3 parts by weight Solvent (MEK / MIBK / toluol) 100-200 parts by weight (Depending on magnetic powder) Recording was performed on each of these seven types of magnetic cards at an optimum recording density current at a recording density of about 200 FCI. FIG. 2 shows the result of measuring the output after demagnetizing this with a barium ferrite magnet (surface magnetic flux density: 1200 gauss). Second
In the figure, ○ indicates the measured value of each magnetic card.For example, in a magnetic card having a magnetic layer with a coercive force of about 1500 Oe, the reproduction output after demagnetization decreases to about 61%. On the other hand, in the magnetic card having the magnetic layer having a coercive force of about 2750 Oe, it is shown that the reproduction output is almost demagnetized to about 98% even after demagnetization. From the curve in Fig. 2, the coercive force required for a magnetic card that is difficult to demagnetize is 20
It can be confirmed that it is more than 00Oe.

Experimental Example II After dispersing and applying Ba ferrite powder with a coercive force of 2000 Oe,
Furthermore, paints in which four types of magnetic materials having different coercive forces were dispersed were applied to fabricate four types of two-layer magnetic cards.
The recording density of about 20 Oe under the coercive force 2000 Oe of these magnetic cards.
The value was recorded at the optimum current value at 0 FCI. This playback output is 100%
And Set the optimum recording current for four different magnetic layers,
FIG. 3 shows the result of measuring the reproduction output after the direct current is erased at the same current value. In FIG. 3, the circles indicate the measured values of each magnetic card, and for example, the coercive force is about
In the magnetic card with 500 Oe intermediate layer, the reproduction output of the high coercive force layer after DC erasing is as high as about 86%, whereas in the magnetic card with the intermediate layer with coercive force about 680 Oe, high coercive force after DC erasing. It has been shown that the playback output of the layer is reduced by about 48%.

Experimental Example III Coercive force of 4000 Oe instead of Ba ferrite powder of 2000 Oe
FIG. 4 shows the results of similar trials of magnetic cards manufactured using Oe Ba ferrite powder as in Experimental Example II.
In FIG. 4, the circles indicate the measured values of each magnetic card. For example, in the case of a magnetic card having an intermediate layer with a coercive force of about 1500 Oe, the reproduction output of the high coercive force layer after DC erasure is about 56.
%, The reproduction output of the high coercive force layer after direct current erasure is reduced to about 25% in the magnetic card having the intermediate layer with the coercive force of about 1900 Oe.

From the experimental results shown in Figs. 3 and 4, when the coercive force of the lower layer (high coercive force layer) is about 2000 Oe to 5000 Oe, the coercive force of the intermediate layer (low coercive force layer) that can be recorded without affecting it Can be confirmed to be from 500 Oe to 1500 Oe.

Next, in order to satisfy the condition of (2) above, the results of experiments performed to confirm the effect when both the high coercive force layer and the low coercive force layer are formed by a coating film in which Ba ferrite powder is dispersed are described. Show.

Example IV In accordance with the present invention, a coating material having the composition shown below was applied onto a white PET paste by a nozzle coater so that the thickness after drying was 10 μm to form a high coercive force layer. The magnetic material of the following composition was changed to Ba ferrite powder with coercive force of 750 Oe to prepare a magnetic coating, and the coating was applied so that the thickness after drying would be 10μ, and the intermediate layer (low coercive force layer) And

Ba ferrite powder (average particle size 0.65μ, H _c = 2800Oe) 100 parts by weight S-REC A 18 parts by weight Nipporan 2304 35 parts by weight Solvent (MEK / MIBK / toluene) 96 parts by weight Comparative Example I Intermediate layer magnetic field of Experimental Example IV with C _o deposition [gamma] F _e2 O ₃ to the body, was fabricated a magnetic card having a two-layer similarly to experimental example IV.

The cross section of the magnetic card of Experimental Example IV is formed by a coating film in which Ba ferrite powder is dispersed in both the high coercive force layer and the intermediate layer (low coercive force layer), and the shape and particle size are almost the same. It was not clear from the secondary electron image of No. 2 that there were two layers. Further, it was not clear from the backscattered electron image (composition image) and the energy dispersive X-ray analysis that the layer had two layers.

On the other hand, in the magnetic card of Comparative Example I, it was possible to easily identify that the magnetic card had two layers due to the shape and particle size of the magnetic material, and that the two layers were obtained from the composition image and the X-ray distribution. .

Finally, an example of a method of using the magnetic recording medium of the present invention as a security card will be described.

In the high coercive force layer 4 of the magnetic recording medium, numerical information A, for example,
If it is used 500 times, the data representing 500 times is recorded as the initial value, and the low coercive force layer 3 records the value information v and the data representing C = F (A, v) as the verification information C. I'll do it.

In a vending machine or the like in which such a security card is used, when the security card is inserted, the numerical information A is read from the high coercive force layer 4 and the low coercive force layer 3 is read.
The value information v and the verification information C are read from the card, the value of the function F (A, v) is immediately calculated, and the value is compared with the read C to verify whether the card is an unaltered regular card. . As a result of the verification, if the card is legitimate, the value information is processed and the number 1 is counted from the number information A.
After re-recording the new numerical information A ′ obtained by subtracting from the high coercive force layer 4, the card is returned to the user.

According to such a usage method, even if only the value information of the security card is rewritten to high value information, the number information A
If the user does not know the function F (A, v) and the function F (A, v) cannot be tampered with. In addition, the structure of the two magnetic layers as in the present invention allows the recording of numerical information in the high coercive force layer and the recording of the value information and the verification information in the low coercive force layer with a difference in coercive force. It is more effective because it can be done using
Since each information cannot be separated by normal reading, this is also effective in preventing information tampering.

EFFECTS OF THE INVENTION The magnetic recording medium of the present invention has the above-described configuration, and therefore, data recording can be easily performed with a normal magnetic head,
Moreover, it is possible to further enhance the protection function for preventing tampering of information.

That is, first of all, both the information recorded in the low coercive force layer and the information recorded in the high coercive force layer are shielded (concealed) by the high magnetic permeability layer. Also, it is possible to record true information having an anti-counterfeit effect.

Secondly, since the high coercive force layer and the low coercive force layer are adjacent to each other and information is recorded against the shield effect against the external magnetic field by the high magnetic permeability layer, the high coercive force layer and the low coercive force layer are formed. Each recording current has a narrow adjustment range, and if the recording current adjustment range is narrow in this way, it becomes more difficult to record the forgery information and the anti-counterfeiting effect is extremely high.

[Brief description of drawings]

FIG. 1 is a partially enlarged sectional view of a magnetic recording medium as one embodiment of the present invention, and FIGS. 2, 3, and 4 show results of various experiments for confirming the effects of the present invention. FIG. 1 ... Protective layer, 2 ... High magnetic permeability layer, 3 ... Low coercive force layer, 4 ... High coercive force layer, 5 ... Substrate.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hiroshi Hosaka 1-5-1 Taito, Taito-ku, Tokyo Within Tokyo Magnetic Printing Co., Ltd. (72) Inventor Norio Yano 2356 Take, Yokosuka, Kanagawa Nippon Telegraph and Telephone Corporation Telephone Corp., Complex Communications Laboratory (72) Inventor, Ginya Ishiguro, Yokosuka City, Kanagawa Prefecture, 2356, Nippon Telegraph and Telephone Corporation Complex Communications Laboratory (72) Inventor, Yuzo Kozo 6-7 Koriyama, Sendai City, Miyagi Prefecture No. Tohoku Kinzoku Kogyo Co., Ltd. (56) Reference JP-A-60-219635 (JP, A) JP-A-61-145727 (JP, A)

Claims (3)

[Claims] 1. A magnetic recording medium in which a high coercive force layer, a low coercive force layer, and a high magnetic permeability layer are sequentially laminated on a substrate, wherein the high magnetic permeability layer is the underlying low coercive force layer and the high magnetic coercive force layer. The high coercive force layer is formed of a material capable of giving a coercive force of 20 Oe or less, which is sufficient to exert a shield effect on the information recorded in the magnetic force layer, and the high coercive force layer has a shielding effect against an external magnetic field by the high magnetic permeability layer. 2000Oe so that information can be recorded with a magnetic head and it is hard to receive accidental demagnetization accidents.
The low coercive force layer is formed of a material capable of giving a coercive force of not less than 5000 Oe or less, and the low coercive force layer is recorded in the high coercive force layer against the shield action against the external magnetic field by the high magnetic permeability layer. A magnetic recording medium formed of a material capable of giving a coercive force of 500 Oe or more and 1500 Oe or less so that information can be recorded by a magnetic head without affecting the information. 2. The magnetic recording medium according to claim 1, wherein the high coercive force layer and the low coercive force layer are formed of a coating film in which Ba ferrite powder is dispersed. 3. The magnetic recording medium according to claim 1, wherein the high coercive force layer and the low coercive force layer are formed of a coating film in which Sr ferrite powder is dispersed.